1. Field of the Invention
The invention relates to heat exchange catheters used for access to the central venous blood supply of a patient.
2. Description of Related Art
Catheters such as central venous catheters are typically used in ICU (intensive care unit) patients, particularly in those patients who have suffered a stroke or other brain traumatic event. The central venous line catheters are typically about 4-12 French in size and consist of a soft, flexible multi-lumen structure extending 8-12 inches. They are usually introduced through the subclavian or jugular vein, and some times in the femoral vein of the patient, serving to provide the caretaker with easy and convenient access to the patient""s central blood supply via the central venous system. In this manner general access to the central blood supply is gained, enabling for example delivery of drugs, infusion fluids or nutrition, along with the gathering of patient blood for blood gas analysis and the like.
In many patients, such as ICU patients, fever is a common occurrence. Fever is particularly likely in neuro-ICU patients, and its onset can exacerbate detrimental effects in the brain. Conventional therapies to control fever include treatment with acetaminophen (Tylenol(trademark)), ibuprofin, cooling blankets, ice water bladder lavages, and ice baths. All of these approaches to cooling a patient require excessive time to cool the patient. Moreover, prior methods do not provide for precise control of patient cooling. As recognized herein, to optimize the advantage of cooling a patient, it is important to cool the patient relatively quickly in a controlled fashion.
Recognizing the above-mentioned deleterious effects of fever in ICU patients and the insufficiencies of present temperature control methods and devices, the present assignee has disclosed, in co-pending patent application Ser. Nos. 09/133,813 and 09/063,984, indwelling catheters that can be implanted in the body of a patient to remove heat from the blood supply of the patient. The indwelling catheters of the above-referenced applications are disposed in a heat exchange relationship with the blood supply, and a coolant is circulated through the catheters in a closed loop. These catheters lower the temperature of body tissue and, as mentioned above, can thereby improve the patient""s medical outcome.
As understood by the present invention, the advantages of the above-referenced cooling catheters can be implemented in a central venous catheter configuration. As mentioned above, central venous catheters are commonly used in many ICU patients, including neuro-ICU patients, and with these combined recognitions, the present invention understands that it would be advantageous to provide a central venous catheter with the additional capability of cooling a patient. In doing so, the present invention satisfies the goals both of conventional central venous catheters as well as providing a means for effectively and precisely managing patient temperature in a single device.
The present invention overcomes the deficiencies of the prior art by providing a central venous line catheter adapted to actively exchange heat with the body of the patient to thereby raise or lower body temperature as required. The central venous line is provided with a heat exchange element disposed in heat exchange relationship with the blood of the patient. The heat exchange element houses a circulating fluid therein, with the fluid being automatically cooled or warmed exteriorly of the patient""s body in accordance with a patient temperature feedback scheme.
By supplementing the known functions of a central venous line catheter with the function of cooling or warming the patient""s blood, the present invention takes advantage of existing access to the venous system and a single incision, reducing the risk of additional complications. The access, typically through the subclavian, jugular or femoral veins, is to the central blood supply, via the central venous system, and is therefore particularly expedient, permitting efficient cooling or warming of patient body temperature. The term central venous system generally relates to the portion of the venous system which returns blood to the right heart, including the inferior and superior vena cava. A particular advantage of the invention is that the cooling function is performed efficiently in tandem with a procedure which is known to be likely attended by fever, thus anticipating such fever and facilitating its control. The heat exchange relationship between the system and the central venous system of the patient can be maintained for a prolonged durationxe2x80x94for example, from about one hour to about twenty-nine days.
The central venous line catheter in accordance with the invention comprises a tubular structure defining a plurality of lumens. At least two of these lumens convey heat exchange fluid to a heat exchange element disposed at a distal, implantable end of the central venous line catheter, while the rest of the lumens serve to provide access to the central blood supply of the patient. The heat exchange element is in fluid communication with a temperature control module via a tubing set which conveys the heat exchange fluid between the components. The temperature control unit, comprising a cooling and/or a heating device, operates in conjunction with a temperature controller to heat or cool the heat exchange fluid depending on a sensed temperature of the patient.
The system of the invention operates to maintain patient temperature at a desired level. Any deviation from the desired level automatically triggers corrective action, such as circulating the cooled heat exchange fluid through the central venous line catheter to contend with the onset of fever. Additionally, the system is equipped with indicators which signal to the caretaker of the patient the sensed deviation, by for example sensing the increased workload of the system, in order to warn of adverse physiological changes besetting the patient.
In accordance with one embodiment, the heat exchange element comprises a pair of axially arranged balloons which communicate with a corresponding lumens serving to supply heat exchange fluid for circulation in the balloons. The lumens and balloons are arranged such that a serial flow pattern between the balloons is established, and preferably, a pattern in which fluid flows from the distal balloon to the proximal balloon. In this manner heat exchange is optimized.
The invention thus provides a system for controlling patient temperature using a central venous line catheter having a heat exchange element. The central venous line catheter is provided with one or more lumens for providing access to the central blood supply of the patient, and with additional lumens for communicating heat exchange fluid to the heat exchange element. Heat exchange fluid temperature is controlled through a feed back loop in which patient temperature is sensed and used to control a temperature control unit comprising a heating device and/or a cooling device in heat exchange relationship with the heat exchange fluid. A tubing set transports the heat exchange fluid between the central venous line and the temperature control unit, with a pump serving to circulate the fluid in a closed fluid circuit in the system.
In accordance with the invention, patient body temperature can be therapeutically reduced by circulating a cooling fluid as the heat exchange fluid in a catheter in a patient-implanted catheter such as a central venous line catheter. Such an application can be attended by the use of warm blankets or other heating means to prevent a shivering response in the patient. Warm blankets will effectively keep the body""s nerve receptors from triggering the shivering response, which would cause warming of the body and reduce the effects of the hypothermia-inducing procedure.